Effect of some spray pyrolysis parameters on electrical and optical properties of ZnS films

Abstract

Polycrystalline ZnS films of cubic phase were prepared by spray pyrolysis on amorphous substrate. The films were found to be uniform and to adhere well to the substrate. The effects of deposition time (10–30 min) and substrate temperature (300–500 °C) on their electrical and optical properties were studied. The resistivity was measured at room temperature using the square four-probe method. The dark resistivity was measured as a function of deposition time and substrate temperature. Optical data were recorded in the wavelength range 200–1000 nm. The effect of deposition time (thickness) on resistivity proved the assumption that the resistivity decreases as the film grows owing to the increase in crystallinity and preferred orientation. The dark resistivity increased as the substrate temperature increased. This may be owing to the decrease in film thickness and improvement in stoichiometry or the decrease in electron density and mobility. Increasing thermal mismatch is another important factor. A considerable difference in transmittance was observed for films prepared at different substrate temperatures. The absorption coefficient was measured and then correlated with the photon energy to estimate the energy gap, which was about the value for the cubic phase with a direct transition.